As disclosed by a patent document 1, as a piston crank mechanism in an internal combustion engine, a multi-link-type piston crank mechanism is commonly known which includes: a lower link supported by a crank pin of a crankshaft; an upper link connecting a first end portion of the lower link to a piston pin; and a control link connecting a second end portion of the lower link to an eccentric shaft part of a control shaft.
In such a multi-link-type piston crank mechanism, a crankshaft and a control shaft are required to be rotatably supported individually. Patent document 1 discloses a bearing structure where the crankshaft is supported between a bulkhead of a cylinder block and a main bearing cap, and a control shaft bearing cap is attached to an underside of the main bearing cap, and the control shaft is supported therebetween.
The control shaft bearing cap has a bearing beam structure where a plurality of bearing caps are connected in a ladder form by a beam part extending in an engine longitudinal direction, and is configured to supply lubricating oil to the control shaft bearing part from an oil gallery formed in the beam part.
A patent document 2 does not relate to a multi-link-type piston crank mechanism, but discloses supporting a main journal part of a crankshaft via half-split main bearing metals, and forming an oil groove extending circumferentially in an inner peripheral surface of the main bearing metals.
For the configuration as in patent document 1 where lubricating oil is supplied to the control shaft bearing part via the inside of the beam, it is necessary to form the control shaft bearing cap in the bearing beam structure, thereby leading to a low flexibility of design. Moreover, the bearing beam structure provided with the oil gallery leads to a complicated configuration.